This invention relates to a pipe joint for a multi-layer composite pipe, and method of forming same.
Plastic pipes are used increasingly in the transportation of gases and liquids, including oils and chemicals, which are under a high pressure within the pipe. Whilst techniques, such as orientation and cross-linking exist to improve the pressure resistance of a exist to improve the pressure resistance of a normal thermoplastic pipe wall, it technically and economically difficult to raise the pressure resistance of the pipe higher than around 15 to 20 bars.
Accordingly, multi-layer composite pipes comprising, for example, a thermoplastic inner layer and, outside it, a reinforcing layer, or a high axial strength inner layer and an outer protective layer, have been proposed for use as high pressure pipes.
Normally the reinforcing layer consists of fibres wound helically around the thermoplastic inner layer. The fibres may be bundled in tape form and the tape matrix fused to the thermoplastic inner layer by the use of heat, for example, as described in EP 0 593 449. The reinforcing layer can also be a conductive layer, for example a metal layer, which is spirally wound or seam welded on top of the thermoplastic layer in order to form a reinforcing metal layer of about 0.2 mm to 5 mm thickness over the thermoplastic layer. The reinforcing layer is preferably covered with another protective thermoplastic layer, which may contain, for example, pigments, antioxidants, fillers, and other modifying components.
Such reinforced multi-layer composite pipes are described, for example, in International Patent Application No PCT/FI96/00359, the entire disclosure of which is incorporated herein by reference for all purposes.
In order to form a firm bond between the reinforcing layer and the inner and outer thermoplastic layers, it is components, which can lose the adhesion-promoting ability if they are in contact with certain liquids, including water. Where the reinforcing layer is a metal layer, this must also be protected from any gases or liquids in the pipe, and from the environment, in order to avoid corrosion problems.
The gas or liquid flowing inside the pipe, and environmental moisture from outside the pipe, cannot normally come into contact with the reinforcing layer or the adhesive components due to the presence of the inner thermoplastic layer and the outer protective thermoplastic layer which together cover the reinforcing layer. However, at the ends of the pipe the continuity of the inner layer and the outer protective layer is disrupted, and therefore pipe connections need to be made in such a way that the reinforcing layer does not come into contact with either the gases or liquids within the pipe, or the outer environmental conditions.
Many solutions to the above problem have been proposed, but all have their drawbacks.
WO92/21908 discloses a pipe connection in which the reinforcing layer becomes thinner over a long surface towards the end of the pipe, and ends a distance from the end of the thermoplastic layer, where an extension is formed. An adaptor is fitted inside the extension, and outside the end of the thermoplastic layer the adaptor is attached, by means of threads, to a steel pipe surrounding the end of the pipe. The adaptor has a conical surface which presses the thermoplastic layer against the inner surface of the outside steel pipe.
The disadvantage of this known pipe connection is that liquid, especially from the outside, but also from the inside of the pipe, can relatively easily enter the end of the reinforcing layer, which, due to a small conical angle, is very large and which thus comprises a great amount of adhesive on the surface of the pipe. A high-pressure liquid flowing inside the pipe can get to the end of the reinforcing layer by going around the end of the thermoplastic layer which is fixed between the adaptor and the steel pipe with compressive forces provided by threads.
In this known solution, the extension at the end of the pipe is formed in a usual manner, ie the extension has a conical surface to which a cylindrical part restricted to the end of the pipe is connected. Such an extension cannot be formed to the part of the pipe which has the reinforcing layer, since due to its characteristics the reinforcing layer does not allow the diameter to increase. Therefore it has been necessary to make the reinforcing layer thinner and to end it before the extension, which thus consists of only the thermoplastic layer. The pipe connection becomes then rather long, and the fitting conical surfaces of the extension and that adaptor, which are the best sealing surfaces of the connection, have a relatively small surface area.
Another solution is provided in European Patent Application No 95 10 4955 in which the ends of composite plastic pipes to be connected are each provided with an extension, and a ring-shaped connecting piece is situated inside the pipes at the extended ends thereof, the connecting piece and the extensions of the pipes to be connected having fitting substantially conical surfaces which extend substantially to the ends of the pipes and from which the connecting piece and the extension are welded together. This system works well with glass fibre reinforced pipes, but is difficult to apply when the reinforcing layer is a metal layer, since it is difficult to form the conical extension without splitting the metal reinforcing layer.
A still further pipe connector is disclosed in DE 44 44 097 which shows an electrofusion coupler which is provided with an annular sealing means to seal the cut ends of the composite pipes. However, in this case, the connection is made only between the thin outer protective thermoplastic layers of the pipes to be connected, and there is no connection between the reinforcing layers. The pipe connection therefore represents a weak point in the pipeline, and is vulnerable to internal pressure and axially, applied forces.
EP-A-0253966 discloses a coupler for a pipe comprising an electrofusion coil and mechanical gripping means, the gripping means being arranged to grip the pipe prior to and during fusion, the fusion joint thereafter providing the effective joint for the pipe.
The entire disclosures of all the abovementioned patents are incorporated herein by reference for all purposes.
In one aspect the present invention provides a joint between a pipe connector and a multi-layer composite pipe, wherein a direct mechanical connection is made to the reinforcing layer, or to the layer of high axial strength, thereby giving a pipe connection of enhanced mechanical strength.
In another aspect, the invention further provides, at least in certain preferred embodiments described herein, a joint between a pipe connector and a multi-layer composite pipe which can:
(i) provide a seal against internal fluids flowing in the pipe;
(ii) provide axial strength, preferably to the level of the pipe itself; and
(iii) provide an environmental seal to prevent contaminants such as dirt from entering the sealing region.
In a further aspect, at least in certain preferred embodiments described herein, the joint of the invention provides a connection to both the inner thermoplastic layer and the reinforcing layer of a multi-layer composite pipe, further improving the quality of the connection.
In a first aspect, the invention provides a joint between an end of a pipe and a connector, wherein the pipe comprises a multi-layer composite pipe having at least one reinforcing layer, or layer of high axial strength, at least one inner thermoplastic layer, and at least one outer protective layer, and wherein the connector comprises:
(i) a hollow, tubular enclosure adapted to receive the pipe;
(ii) fusion means adapted to make a fusion connection with the inner thermoplastic layer of the pipe; and
(iii) mechanical gripping means adapted to grip the reinforcing layer or hugh axial strength layer of the pipe;
the fusion means and mechanical gripping means being disposed within the enclosure and the enclosure being adapted, in use, to apply a constraining forge to the mechanical gripping means, characterised in that the thermoplastic layer extends beyond the end of the protective layer, in that the fusion means and mechanical gripping means are axially spaced within the connector, and in that the axial strength of the joint is provided more by the mechanical gripping means than said fusion connection.
Preferably the connector further comprises sealing means disposed within the enclosure and adapted to form an environmental seal with the outer protective layer of the pipe, the enclosure being adapted, in use, to apply a constraining force to the sealing means.
In a second aspect, the invention provides a method of forming a connection to a multilayer composite pipe, the pipe comprising at least one reinforcing layer, or layer of high axial strength, at least one inner thermoplastic layer and at least one outer protective layer, wherein at least the outer protective layer of the composite pipe is cut back in order that circumferential surfaces of the inner thermoplastic layer, and the reinforcing layer, or high axial strength layer, are exposed for connection by a connector comprising:
(i) a hollow, tubular enclosure adapted to receive the pipe;
(ii) fusion means adapted to make a fusion connection with the inner thermoplastic layer of the pipe; and,
(iii) axially spaced from the fusion means, mechanical gripping means adapted to grip the reinforcing layer of the pipe;
the fusion means and mechanical gripping means being disposed within the enclosure and the enclosure being adapted, in use, to apply a constraining forte to the mechanical gripping means, the axial strength of the joint being provided more by the mechanical gripping means than said fusion connection.
Preferably the fusion means, mechanical gripping means and sealing means are disposed in recesses in the tubular enclosure such that the sealing means is nearest to the and of the tubular enclosure, followed by the mechanical gripping means, and then the fusion means.
The hollow, tubular enclosure can comprise a plastics or a metal body, or may be a composite construction, with plastics and reinforcement layers. The reinforcement can, for example, comprise a sleeve or grid formed from metallic materials, or it can comprise reinforcing fibres. In manufacturing a hollow, tubular enclosure reinforced with fibres, the reinforcing fibres can be wound on a preform and later provided with a plastics outer skin. Alternatively, the fibre reinforcement can comprise a three dimensional preform, which maintains its shape, and comprises fused plastics coated fibres. The preform can be set into a mould cavity and the spaces or interstices in the preform filled with a plastics matrix material by, for example, injection moulding, to give an oriented hollow, tubular enclosure as described in PCT/EP96/02801.
The tubular enclosure may also comprise a recoverable material, and, for example, the tubular enclosure may be formed from an expanded cross-linked polymeric material which is xe2x80x9cheld-outxe2x80x9d on a removable core or supporting device. The tubular enclosure can be an integral body, or can be composed of two or more hollow members which are threaded, in order that they can be screwed together, or which have co-operating annular projections or depressions enabling them to be a snap-fit together.
In preferred embodiments, the action of screwing or pushing the component members of the tubular enclosure together acts to apply, or to increase, the constraining force in the mechanical gripping means and the sealing means. For example, the component members of the tubular enclosure can have co-operating conical surfaces which are forced together in a ramp or wedging action in order to apply radially inwardly directed forces on the mechanical gripping means and the sealing means. In these embodiments, it will be apparent that the walls of the tubular enclosure would need to be, at least to a small sextant, inwardly deformable.
In certain embodiments, the positions of the sealing means and the mechanical gripping means can be interchanged so that the mechanical gripping means is nearest to the end of the tubular enclosure, for example, where the tubular enclosure is provided with axial slits at its end section to facilitate inward deformation.
The fusion means can comprise a connector whereby a pipe is fused or xe2x80x9cweldedxe2x80x9d to another component by the action of heat. Any suitable fusion means may be used, although electrofusion means comprising an electrical heating element which may be a resistance or an induction heating element is preferred. The electrofusion means can, for example, comprise a fitting comprising an electrical conductor element, for example, a metal coil, ring, serpentine ring, expanded mesh, or other suitably shaped member, which is located adjacent to, or embedded in, a layer of fusible thermoplastic polymeric materials. The electrical conductor element may be energised, for example, by passage of an electric current therethrough, or by inductive heating, in order to melt the adjacent thermoplastic material and form a fusion bond with the outer surface of the inner thermoplastic layer of the composite pipe. The invention is not restricted to the use of electrofusion means, however, and for example other fusion techniques such as friction welding of components or the use of pre-heated tools inside the connector, may be used as appropriate.
The fusible thermoplastic polymeric materials of the electrofusion means can comprise, for example, a polyolefin, for example, polyethylene, polypropylene, polybutylene, and higher olefinic polymers; co-polymers of ethylene, propylene and butylene with each other and with olefinically unsaturated monomers; olefinically unsaturated aromatic polymers such as polystyrene and styrene copolymers; and polymers and co-polymers of vinyl monomers such as ethylene vinyl acetate co-polymers, polycarbonates, and like materials. Polyethylene is the preferred fusible polymeric material particularly where polyethylene pipes are to be joined. If desired, the fusible thermoplastic polymeric material can comprise a modified polyolefin material, for example, an anhydride modified polyethylene, or the material can comprise a cross-linking agent which reacts during or after the fusion bonding step to cross-link the polymeric material and possibly the adjacent surface of the pipe, Modified polyolefins are particularly useful in joining polyolefin surfaces of dissimilar composition. Suitable modified polyolefin materials include, for example, alpha olefin polymers and co-polymers comprising up or 10% by weight of an olefinically unsaturated carboxylic acid or an anhydride thereof, such as, for example, acrylic acid. maleic acid, itaconic acid, and succinic acid, or their anhydrides, as co-polymer or graft co-polymer components.
If desired, the fusible thermoplastic polymeric material can comprise one or more fillers, and, for example, it can comprise fillers which react and can reach high temperatures when exposed to infra-red radiation or electromagnetic radiation, for example, stainless steel fibres, as described in PCT/EP96/02801. The use of such fillers to assist, or instead of, the fusion means described above is included within the invention.
The mechanical gripping means can, for example, comprise a series of two or more toothed segments which are radially disposed around the connector and are capable, in use, of contacting and gripping the reinforcing layer of the composite pipe. The mechanical gripping means are preferably formed from a hard, metallic material or from an engineering plastics material such as an acetal resin. The teeth of the mechanical gripping means can, if desired, be sharp enough to penetrate the outer protective layer and/or the reinforcing layer of the composite pipe, in order to improve the connection thereto. Where more than one reinforcing layer is present in the multi-layer composite pipe, the gripping means preferably contacts and gripe the innermost reinforcing layer. The segmented gripping means can, if desired, be provided with a frusto-conical outer surface which is co-operable with a frusto-conical inner surface of the tubular enclosure to improve the gripping action and resist axial pull-out.
Other forms of mechanical gripping means can be envisaged, for example, the teeth could be replaced by roughened surfaces, or the gripping means could comprise a resilient split ring, or similar component. In certain types of multi-layer, composite pipes, for example, as described in PCT/FI96/00359, the surface of the reinforcing layer may not be smooth, and this roughness or undulation can assist the gripping action of the gripping means.
In a further embodiment, the mechanical gripping means can comprise a ring or a series of arcuate segments, provided with helical threads which can be screwed on to the reinforcing layer of the pipe and form co-operating threads thereon. This can be readily accomplished where the reinforcing layer comprises, for example, an aluminium layer. The use of threaded mechanical gripping means provides the further advantage that, with appropriate design, it may be possible to re-enter the joint by rotating the tubular enclosure. It may also be possible to pre-assemble a pipeline, with a number of joints, before installing the pipeline in a trench and before fusion, because the threaded mechanical gripping means would provide sufficient axial strength for the installation. If adjustments to the pipeline need to be carried out, these can be done before fusion. The final fusion step can then be accomplished in the trench with the pipeline in the desired position. Simple removal of an installed joint would also be possible by heating the fusion area to the melt temperature and rotating the tubular enclosure.
Any suitable sealing means may be provided to form an environmental seal between the outer protective layer of the pipe and the hollow, tubular enclosure of the pipe connector. Preferably, however, the sealing means comprises one or more sealing rings, for example, gaskets or O-rings , which may be located in one or more recesses in the inner surface of the tubular enclosure. The sizes of the O-ring and any recess in the enclosure are arranged to be such that, in use, the enclosure applies a constraining force on the O-ring in order to force it into sealing contact with the outer surface of the outer protective layer of the composite pipe.
An advantage of the present invention is that it is not necessary to form an environmental seal to the outer protective layer of the pipe by electrofusion means. This enables certain embodiments of a pipe connector of the invention to be used to connect a multi-layer composite pipe having a soft outer protective layer, for example, as described in International Patent Application No PCT/EP96/02801 and in Finnish Application No 955960, the entire disclosures of which are incorporated herein by reference for all purposes, which would not be possible with a conventional electrofusion coupler.
Other types of sealing means may also be used. For example, if the outer protective layer of the plastics pipe is relatively soft, the use of an O-ring may, in some instances, give rise to an unacceptable level of creep. In such cases, the O-ring could be replaced by an annular ring of a relatively soft viscous sealing material such as, for example, a mastic, or by an adhesive elastomeric sealant, or a hot melt adhesive. Where a sealing material having significant room temperature tack is used, the recess in the inner surface of the tubular enclosure is preferably of such a size that the sealing material is not brought into contact with the outer layer of the pipe until a constraining force is applied. Where the sealing material is heat activatable, the necessary heat may be supplied by exterior heating or by the heat generated by the fusion means.
The pipe connector of the present invention may be provided as an assembly, into which a prepared end of the composite pipe is simply inserted, or may be provided as two or more separate components which are individually installed. For example, the fusion means can be integral with the tubular enclosure, or provided as a separate component. By installing the component separately they can be individually inspected to ensure that, for example, the fusion joint has been correctly formed, before the tubular enclosure is installed over the other components of the connector. Preferably the axial strength of the tubular enclosure is greater than the axial strength of the fusion means, in order the tensile forces are transferred from the fusion joint to the tubular enclosure.
In many cases it is desirable that the pipe connector should provide electrical continuity across the connection, especially between the reinforcing metal layers of two composite pipes to be connected. Such composite pipes are described in International Patent Application No PCT/FI96/00359 mentioned hitherto. The pipe connector of the present invention provides a particularly simple way of maintaining electrical continuity, and this is a preferred and further aspect of the invention. Electrical continuity can be provided, for example, by connecting the ends of the electrofusion coil, either before or after fusion, to adjacent ends of the metal reinforcing layer. An electrofusion oil can, for example, be provided with terminal which may he connected, either directly, or through the mechanical gripping means, to the reinforcing metal layers. In a preferred embodiment, the ends of the electrofusion coil are each provided with a terminal which is received in a socket in an adjacent segment of the mechanical gripping means Electrical continuity is thereby provided through the mechanical gripping means which is capable of penetrating and piercing any oxide layer on the reinforcing metal layer, and thence through the electrofusion coil to the metal layer on the composite pipe to be connected. Other methods of providing electrical continuity can also be provided, for example, the mechanical gripping means could be directly connected over the fusion means or via the tubular enclosure if the enclosure if formed from a conductive material
In preparing the multi-layer composite pipe for connection, the outer protective layer and the reinforcing layer, where present, are preferably each cut back in order that circumferential surfaces of the inner thermoplastic layer, and the reinforcing layer are exposed for connection. Preferably the lengths of the inner thermoplastic layer and the reinforcing layer thereby exposed are from 20 to 200% of OD, where OD is the outer diameter of the pipe.
In preparing the reinforcing layer for connection, in some embodiments it may be desirable to form an upstanding projection at the out back edge of the reinforcing layer for extra strength, or to provide easier electrical connection. Whilst the invention will normally be applied to multi-layer composite pipes in which the reinforcing layer is flat, it will be apparent that it would equally be possible to form a connection with pipes in which the reinforcing layer is corrugated.
In a still further embodiment, it may be possible, in preparing the pipe end for connection, to turn over the inner thermoplastic layer so that it lies on top of and overlaps the reinforcing layer for a short distance at the end of the pipe. This may make electrofusion easier since the inner thermoplastic layer would then be doubled in thickness and also supported by the reinforcing layer, and could enhance the gripping effectiveness of the mechanical gripping means.
Whilst it would normally be preferred to cut back the outer protective layer in order to expose the reinforcing layer to the mechanical gripping means, this is not essential, and, for example, it may be possible to use a gripping means having sharpened teeth which could penetrate the outer protective layer in order to make contact with and grip the reinforcing layer through the protective layer.
The multi-layer, composite pipe of the invention has been mostly described hitherto with reference to at least three distinct layers; the outer protective layer, the reinforcing layer or layer of high axial strength, and the inner thermoplastic layer it will be apparent, however, that in certain embodiments, two or more layers of the pipe can be combined, and/or one of the layers can have a dual function. For example, the invention also includes a connector for joining a multi-layer pipe wherein the functions of the inner thermoplastic layer and the reinforcing layer or layer of high axial strength of the pipe are fulfilled by a single thermoplastic layer which is, for example, cross-linked and/or oriented in the axial direction to give a very high axial strength. In such a pipe, preparation merely comprises stripping back the outer protective layer to expose the cross-linked and/or oriented inner layer for fusion and, if necessary, for mechanical connection to the gripping means, if this is not able to penetrate the outer protective layer. An example of a pipe which can be connected in this way is a cross-linked, axially oriented, polyethylene (PEXO) pipe, with an outer protective layer having an axial strength less than that of the cross-linked, oriented polyethylene layer. The connection of such pipes is expressly included within the invention.
The pipe connection of the invention can, for example, be sued in an in-line coupler, for connecting two similar pipes in line, a bend, for connecting two similar pipes arranged at an angle, a transition coupler, for connecting pipes of different diameters, or in a fitting for connecting a multi-layer composite pipe to other fittings or pipes, wherein the fitting is provided, at its end remote from the connector of the invention, with other connecting means, for example, a screw-threaded end, a conventional electrofusion means, a butt fusion end, a flanged end or similar connecting means.